Most general purpose ladders fall into one of two categories. The first type of ladder, the extension ladder, comprises upper and lower ladder sections, each comprised of a pair of generally parallel, spaced-apart rails having a plurality of rungs extending therebetween. The upper and lower extension ladder sections are slidebly mounted such that the upper ladder section is slidebly extensible with respect to the lower ladder section. In this manner, the upper ladder section can be extended, either fully or partially, to provide additional height when in use, and then slidebly retracted until the two ladder sections are coextensive for storage.
The second type of ladder is the so-called "stepladder." The stepladder comprises a ladder section with generally parallel rails having a plurality of rungs extending therebetween. A bracing frame has an upper end attached to the upper end of the ladder section and extends downwardly and outwardly therefrom. A pair of standoff arms are connected to intermediate points of the ladder section and the bracing frame to hold the ladder section and the bracing frame in predetermined angular relation. When erected, the stepladder is configured generally like an "A."
Both the extension ladder and the stepladder have their own advantages and disadvantages. The extension ladder can be extended to heights of fifteen to twenty feet or more for use but then retract to a relatively manageable eight to ten feet in length for transport and storage. However, the extension ladder suffers the disadvantage that it depends for support upon its upper end resting against a suitable support structure, e.g., a wall or roof. The stepladder, on the other hand, is freestanding such that it can be used in locations where there is no suitable support structure against which the upper end of an extension ladder could rest. However, the stepladder suffers the disadvantage that it is typically limited to heights of six to ten feet. Further, since the user typically cannot stand atop the stepladder, or even on the highest rung of the stepladder, the height accessible by a stepladder is even further reduced. Providing stepladders in taller heights is generally impractical, because longer stepladders would be unacceptably awkward to transport and store. In addition, taller stepladders are more susceptible to toppling in a lateral direction and hence must have a wider base. However, the wider base would again be disadvantageous in terms of transporting and storing the ladder.
There are many applications for which neither a stepladder nor an extension ladder are suitable. It is often desirable, for example, to gain access to the ceiling of a two story foyer, or to a cathedral or vaulted ceiling, at locations remote from the vertical walls, such as for changing light bulbs or installing or repairing light fixtures or ceiling fans. In such applications an extension ladder is unsuitable because there is usually no nearby wall structure against which the upper end of the extension ladder can be leaned. On the other hand, a stepladder, which is not dependent upon the presence of a suitable wall structure for support, is not tall enough to provide access to such tall ceilings.
Thus there is a need for a ladder which combines the height of an extension ladder with the freestanding design of a stepladder.